The best way to think about a Frame is like the frame that you would
plot around a graph. In two dimensions, you would have an ``'' and
a ``
'' axis, a title on the graph and labels on the axes, together
with an indication of the physical units being plotted. The values
marked along each axis would be formatted in a human-readable way. The
frame around a graph therefore defines a coordinate space within which
you can locate points, draw lines, calculate distances, etc.
An AST Frame works in much the same way, embodying all of these concepts and a few more. It also allows any number of axes, which means that a Frame can represent coordinate systems with any number of dimensions. You specify how many when you create it.
Remember that the basic Frame we are considering here is completely
general. It knows nothing of celestial coordinates, for example, and
all its axes are equivalent. It can be adapted to describe any general
purpose Cartesian coordinate system by setting its attributes, such as
its Title and axis Labels, etc. to appropriate values.
AST A Library for Handling World Coordinate Systems in Astronomy